JP5184154B2 - Flowmeter - Google Patents

Description

  The present invention relates to a flow meter, and more particularly to a flow meter configured to detect a rotational speed of a rotor that rotates in accordance with a flow rate of a fluid to be measured using a pickup that magnetically detects the rotational speed.

  For example, in a turbine-type flow meter, an impeller (rotor) having a plurality of blades on the outer periphery of a hub is rotatably supported in a flow path, and the impeller rotates according to the flow rate of a fluid to be measured flowing through the flow path. The flow rate measurement is performed by detecting the accompanying magnetic change with a pickup (see, for example, Patent Document 1).

  A pickup coil is used as a rotation detecting means used in this type of turbine flow meter. In a turbine-type flow meter, a pickup coil is provided in the flow meter body facing the outer periphery of the impeller, and the impeller blades made of magnetic material change the magnetic resistance of the magnetic circuit by crossing the magnetic field of the pickup coil. A detection pulse is generated by generating an induced voltage.

Then, the calculation unit of the flow meter counts the flow rate pulse obtained from the detection signal output from the pickup coil, and obtains the instantaneous flow rate and the integrated flow rate from the count value per unit time.
Japanese Patent Laid-Open No. 2003-166861

  As described above, in the flowmeter that detects the rotation of the impeller using the pickup, the voltage value of the detection signal output from the pickup increases according to the flow rate of the fluid to be measured. For this reason, in the method of generating a flow pulse when the signal waveform of the detection signal output from the pickup is equal to or greater than a predetermined threshold, in order to accurately detect an abnormality in the flow meter, for example, to eliminate the influence of noise If the threshold value is set high, the voltage value output from the pickup at a small flow rate falls below the threshold value, resulting in a problem that the small flow rate cannot be measured.

  In addition, when the threshold is set small so that small flow rate can be measured, the noise superimposed on the detection signal will also be detected as a signal, and the abnormality cannot be detected quickly and the abnormality has occurred There is a risk that the flow rate will be measured incorrectly.

  Therefore, in view of the above circumstances, an object of the present invention is to provide a flow meter that solves the above problems.

  In order to solve the above problems, the present invention has the following means.

The present invention includes a rotor formed of a magnetic material that rotates according to a flow rate of a fluid to be measured flowing in a flow path,
A pickup that forms a magnetic field in a region where the rotor rotates, detects a magnetic change accompanying the rotation of the rotor, and outputs a detection signal;
In a flowmeter comprising flow rate calculation means for calculating the flow rate of the fluid to be measured flowing in the flow path from the detection signal output from the pickup,
Voltage detection means for detecting a voltage value of a detection signal output from the pickup;
Period calculating means for calculating the period of the basic waveform from the minimum voltage value or the maximum voltage value of the detection signal obtained based on the voltage value detected by the voltage detecting means;
Noise component frequency calculation means for calculating the frequency of the noise component obtained based on the voltage value detected by the voltage detection means;
When the frequency of the noise component is larger than a predetermined abnormality judgment value, a correction means for correcting the measurement waveform of the detection signal to a sine waveform obtained from the frequency of the basic waveform and the peak value of the measurement waveform;
With
The flow rate calculation means measures the flow rate of the fluid to be measured flowing in the flow path based on the detection signal when the frequency of the noise component calculated by the noise component frequency calculation means is equal to or less than a predetermined abnormality determination value. the Rukoto to be measured, is intended to solve the above problems.

According to the present invention, when the frequency of the noise component calculated by the noise component frequency calculating means is equal to or less than a predetermined abnormality determination value, the flow rate of the fluid to be measured flowing in the flow path is measured based on the detection signal, When the frequency of the noise component is greater than the predetermined abnormality judgment value, the noise superimposed on the detection signal is used to correct the measurement waveform of the detection signal to the sine waveform obtained from the frequency of the basic waveform and the peak value of the measurement waveform. It is possible to expand the flow rate measurable range widely from the low flow rate range to the high flow rate range.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a view showing an embodiment of a turbine type flow meter according to the present invention, wherein (A) is a longitudinal sectional view of the turbine type flow meter, and (B) is a pressure distribution diagram in a flow path. As shown in FIG. 1A, the turbine type flow meter 10 is configured by rotatably providing an impeller (rotor) 16 in a flow path 14 formed in the meter body 12. The impeller 16 is inserted into a rotation shaft 18 supported at the center of the flow path 14 and is rotatably supported. The impeller 16 rotates at a rotational speed proportional to the flow rate of the fluid to be measured flowing in the flow path 14.

  Both ends of the rotary shaft 18 are held by shaft support members 20 and 22 fitted in the flow path 14. The rotating shaft 18 includes an upstream cone 24 positioned on the upstream side of the impeller 16, a downstream cone 26 positioned on the downstream side of the impeller 16, and between the upstream cone 24 and the downstream cone 26. And a cylindrical shaft 28 interposed therethrough.

  The impeller 16 is provided with a plurality of blades (blades) 32 made of a magnetic material radially on the outer periphery of the hub 30 and is slidable on the outer periphery of the cylindrical shaft 28 at the center of the hub 30. A bearing member 34 is integrally provided. The hub 30 of the impeller 16 has an axial thickness T that is smaller than the distance L between the upstream cone 24 and the downstream cone 26 (T <L).

  Accordingly, the impeller 16 is supported such that the upstream and downstream end surfaces 30a and 30b of the hub 30 are opposed to the upstream cone 24 and the downstream cone 26 via the gap S = (LT) / 2. , And are supported in a floating state not in contact with the upstream cone 24 and the downstream cone 26.

  For this reason, the impeller 16 is supported so that the bearing member 34 can rotate in a floating state by the cylindrical shaft 28 and can slide in the axial direction (upstream side or downstream side) of the cylindrical shaft 28 by the gap S. Has been.

  The upstream cone 24 includes a hollow shaft portion 24a that is in contact with the shaft support member 20, and a cone-shaped cone portion 24b that is inclined toward the downstream side so as to have a larger diameter than the outer diameter of the shaft portion 24a. And a bearing portion 24c embedded in the end surface of the cone portion 24b and abutted against the upstream end portion of the cylindrical shaft 28.

  The downstream cone 26 includes a hollow shaft portion 26a that is in contact with the shaft support member 22, and a cone-shaped cone portion that is inclined toward the upstream side so as to be larger in diameter than the outer diameter of the shaft portion 26a. 26b, a bearing portion 26c embedded in the end surface of the cone portion 26b and in contact with the downstream end portion of the cylindrical shaft 28, and a pressure introducing hole 26d for introducing downstream pressure to the end surface of the cone portion 26b. .

  The rotary shaft 18 passes through the shaft portion 24 a of the upstream cone 24 and the shaft portion 26 a of the downstream cone 26 and is inserted into the shaft support members 20 and 22. Both ends of the rotating shaft 18 are male threads, and nuts 35a and 35b are screwed into the shaft support members 20 and 22.

  The pressure introduction hole 26d penetrates the cone part 26b in the axial direction, and introduces the downstream pressure into the gap S formed between the downstream end surface 30b of the hub 30 of the impeller 16 and the cone part 26b. Thereby, the impeller 16 is maintained in a floating state in which the upstream pressure and the downstream pressure acting on the upstream and downstream end faces 30a and 30b of the hub 30 are balanced.

  As shown in FIG. 1B, the pressure distribution in the flow path 14 is P1 upstream of the upstream cone 24, P2 near the outer periphery of the blade 32 of the impeller 16, and downstream of the downstream cone 26. P3 and P4 are satisfied (P1> P3 (P4)> P2). Further, on the upstream side of the impeller 16, the pressure changes from P1 to P2, and on the downstream side of the impeller 16, the pressure changes from P2 to P3. The pressure introduction hole 26d introduces the pressure P3 toward the downstream end surface 30b of the hub 30 of the impeller 16 to balance the pressure acting on the upstream and downstream end surfaces 30a, 30b of the hub 30.

  A pickup 36 is attached to the inside of the wall surface of the flow path 14 adjacent to the outer peripheral end of the blade 32 of the impeller 16. The pickup 36 is connected to a control circuit 38 that performs flow rate calculation.

  The pickup 36 has a coil that forms a magnetic field toward the flow path 14 around which the impeller 16 rotates. When the blade 32 of the impeller 16 formed of a magnetic material crosses the magnetic field, the magnetic resistance of the magnetic circuit. Changes to generate an induced voltage in the coil, thereby outputting a detection signal.

  The control circuit 38 counts the flow rate pulse obtained from the waveform of the detection signal output from the pickup 36, and calculates the instantaneous flow rate and the integrated flow rate from the count value per unit time.

  In the memory 39 of the control circuit 38, a control program (flow rate calculating means) for calculating the flow rate of the fluid to be measured flowing in the flow path 14 from the detection signal output from the pickup 36, and the detection signal output from the pickup 36 are stored. A database (crest value-frequency storage means) for storing the correspondence between the crest value and the frequency, and a crest value corresponding to the frequency of the detection signal are read from the database, and the crest value of the detection signal output from the pickup 36 is read. A control program (determination means) that determines whether or not the peak value is within a preset range, and if it is determined that the peak value is not within the range, an abnormal signal is output. A control program (output means) to be output is stored.

  Here, the flow measurement of the turbine type flow meter 10 configured as described above will be described. FIG. 2 is a view showing a flow rate measuring method by the impeller 16, (A) is a longitudinal sectional view showing a state in which the impeller 16 is floated, and (B) is output from the pickup 36 corresponding to (A). It is a wave form diagram of a detection signal.

  The fluid to be measured that has flowed into the flow path 14 of the meter body 12 is guided toward the blade 32 of the impeller 16 by the upstream cone 24 and moves in the downstream direction while pressing the blade 32 in the rotation direction. Then, the fluid to be measured flows through the impeller 16 and then flows downstream along the downstream cone 26, but a part of the fluid to be measured passes through the pressure introduction hole 26 d to the downstream end face 30 b of the hub 30 of the impeller 16. Move towards.

  As a result, the secondary pressure acts on the downstream end face 30b of the hub 30 to push the impeller 16 back slightly upstream. Therefore, as shown in FIG. 2A, the impeller 16 is supported in a floating state at a substantially intermediate position between the upstream cone 24 and the downstream cone 26.

  The blades 32 of the impeller 16 in a floating state are positioned so as to face the lower side of the pickup 36 and rotate so as to cross the magnetic field 40 from the pickup 36. As a result, as shown in FIG. 2B, the detection signal of the pickup 36 is output as a sine wave having a constant period. Further, since the blade 32 of the impeller 16 rotates at a position closest to the pickup 36, the peak value V1 of the detection signal becomes equal to or greater than a specified value.

  FIG. 3 is a waveform diagram of a detection signal output from the pickup 36. As shown in FIG. 3, when a small flow rate is measured, the detection signal output from the pickup 36 has a frequency f1 and a peak value V1 as shown by a solid line. Further, when a large flow rate is measured, the detection signal has a frequency of f2 and a peak value of V2, as indicated by a broken line. The correspondence relationship between these measured values is that the frequency is f1> f2 and the crest value is V1> V2, so that the frequency and crest value tend to increase as the flow rate increases, and the frequency and crest value increase as the flow rate decreases. High prices tend to decrease.

  Therefore, the frequency and peak value of the detection signal of the pickup 36 change in proportion to the flow rate. The control circuit 38 counts the flow rate pulse obtained from the detection signal output from the pickup coil 36 and calculates the instantaneous flow rate and the integrated flow rate.

  Here, the correspondence between the peak value of the detection signal output from the pickup 36 and the frequency will be described. As shown in FIG. 4, the detection signal output from the pickup 36 has a proportional relationship between frequency and voltage (crest value) as can be seen from the graph A indicating the normal characteristics, and the coil of the pickup 36 increases as the frequency increases. There is also a tendency that the voltage induced by the voltage increases. Data indicating the normal characteristics of the graph A is stored in the memory 39 in advance.

The relationship between the frequency and voltage (peak value) shown in graph A can be expressed as the following equation.
E = a · f (1)
In the above equation, E is the voltage value (V) of the detection signal output from the pickup 36, f is the frequency of the detection signal output from the pickup 36, and a is a constant that varies depending on the aperture of the flow meter.

  According to (1) above, the voltage value of the detection signal from the pickup 36 when the fluid to be measured is not flowing is zero V, but the impeller 16 slightly reciprocates in the axial direction due to the influence of vibration or the like. Electromotive force is generated in the coil of the pickup 36. At that time, since the blade 32 made of a magnetic material slightly reciprocates below the pickup 36 in the impeller 16, since the change in the magnetic field is small, the excitation electromotive force (voltage value) generated in the coil of the pickup 36 is small. ) Is small. However, since the cycle of the reciprocating motion of the impeller 16 is small, the frequency of the detection signal output from the pickup 36 is large.

  FIG. 5 shows the state at this time in comparison with the graph A. FIG. As shown in FIG. 5, it is possible to determine whether there is an abnormality depending on where the peak value (voltage) obtained from the detection signal for the graph A based on the normal signal and the frequency are located.

  Further, as shown in FIG. 5, the control circuit 38 sets a boundary line B (indicated by a one-dot chain line) that determines a predetermined range for the graph A. This boundary line B is an imaginary line for dividing an area defined by an allowable range parameter input in advance. When the position of the peak value-frequency output from the pickup 36 falls within the boundary line B, it is distributed in the vicinity of the graph A, so that it is determined to be normal and is output from the pickup 36. When the peak value-frequency position is located outside the range of the boundary line B, it is determined to be abnormal because it is far from the graph A.

  Next, the flow rate measurement control process 1 executed by the control circuit 38 will be described with reference to the flowchart shown in FIG. The control circuit 38 measures and stores the frequency from the period of the detection signal (flow rate measurement signal) output from the coil of the pickup 36 in S11 of FIG. Subsequently, in S12, the voltage (crest value) of the detection signal output from the coil of the pickup 36 is measured and stored.

  In next S13, the data of the graph A that defines the correlation between the peak value and the frequency stored in the memory 39 is read, and the frequency and voltage measured in S11 and S12 are compared with the graph A (determination means).

  In the next S14, it is determined whether or not the voltage (crest value) with respect to the frequency measured in S11 and S12 is within the allowable range for the graph A (the range defined by the boundary line B). If the measured frequency and voltage are within the allowable range, the process proceeds to S15, where the currently detected signal is determined as a normal signal, a flow rate pulse is generated, and a flow rate calculation process (flow rate pulse integration process) is performed.

  In S14, if the measured frequency and voltage are located outside the allowable range, the process proceeds to S16, where the currently detected signal is determined to be an abnormal signal, and the flow rate calculation process is not performed. Is set to zero (output means). The processes of S11 to S16 are repeatedly executed for each period of the detection signal.

  Therefore, the frequency obtained from the interval (cycle) between the minimum value of the detection signal (flow rate measurement signal) output from the pickup 36 as a sine wave and the next minimum value, and the minimum value and maximum value of the detection signal (flow rate measurement signal). By comparing the correspondence relationship with the peak value (voltage) obtained from the difference with the graph A and determining whether or not the signal is within the allowable range of the graph A, the signal is a normal signal or abnormal. It is possible to determine whether the signal.

  In other words, since the flow rate can be measured without setting a threshold value for the detection signal output from the coil of the pickup 36, even when measuring a small flow rate region where the frequency and peak value (voltage) are small, it is superimposed on the detection signal. It is possible to determine the presence or absence of abnormality without being affected by the generated noise. Thereby, it becomes possible to stably perform a wide range of flow rate measurement from a small flow rate range to a high flow rate range, and more accurate flow rate measurement can be performed.

  Here, a modified example of the pickup 36 will be described. FIG. 7 is a view showing a modification of the pickup 36.

  As shown in FIG. 7, the pickup 36 is obtained by winding a coil 36b around a core (iron core) 36a, and the core 36a and a magnet 36c disposed on the core 36a constitute a magnetic circuit. The magnetic field 40 passing through the core 36a and the magnet 36c extends to the flow path 14 where the blade 32 of the impeller 16 rotates.

  The blades 32 of the impeller 16 are formed of a magnetic material, and a plurality of (eight in the present embodiment) radially protrude from the outer periphery of the hub 30 at equal intervals. When the fluid to be measured flows through the flow path 14, a rotational force according to the flow rate (flow velocity) of the fluid to be measured acts on the blade 32, and the impeller 16 rotates. Therefore, the eight blades 32 of the impeller 16 cross the magnetic field 40 from the pickup coil 36 at a cycle according to the rotation speed.

  As a result, an induced voltage is generated in the coil 36 b of the pickup 36, and a detection signal having a frequency corresponding to the rotational speed of the impeller 16 is output to the control circuit 38. In the pickup 36, the magnetic field 40 from the magnet 36 c is formed in the flow path 14 through the core 36 a, so that the magnetic field strength in the flow path 14 is increased and the magnetic field change accompanying the rotation of the impeller 16 is correspondingly increased. The voltage increases and the peak value of the detection signal detected by the coil 36b increases.

  FIG. 8 is a diagram illustrating a waveform in a state where noise is superimposed on the detection signal output from the pickup 36. As shown in graph C of FIG. 8, the detection signal has a sine waveform. However, when noise having a smaller amplitude than this sine waveform is superimposed, it is difficult to accurately determine the period and peak value of the sine waveform. In the graph C, it is assumed that the minimum voltage value Vmin1, the maximum voltage value Vmax, and the minimum voltage value Vmin2 are detected in the order including noise.

  In the memory 39 of the second embodiment, a control program (voltage detection means) for detecting the voltage value of the detection signal output from the pickup 36, and the detection cycle of the minimum voltage value and the maximum voltage value are calculated from the detected voltage value. And a control program (period calculation means) to be stored. The control circuit 38 reads the control program in the memory 39 and performs an arithmetic process as shown in FIG. 9, so that accurate flow measurement can be performed without being affected by noise.

  Here, the flow rate measurement control process 2 executed by the control circuit 38 of the second embodiment will be described. The control circuit 38 measures the minimum voltage value Vmin1 of the detection signal output from the coil 36b of the pickup 36 in S21 shown in FIG. As this minimum voltage value Vmin1, the voltage value detected immediately before is stored in the memory 39, and when the voltage value detected this time is smaller than this voltage value, the minimum voltage value is updated and detected immediately before. When the voltage value detected this time is larger than the voltage value, the voltage value detected immediately before is stored as the minimum voltage value Vmin1.

  Subsequently, in S22, the maximum voltage value Vmax of the detection signal output from the coil 36b of the pickup 36 is measured and stored. As this maximum voltage value Vmax, the voltage value detected immediately before is stored in the memory 39, and when the voltage value detected this time is larger than this voltage value, the maximum voltage value is updated and detected immediately before. When the voltage value detected this time is smaller than the voltage value, the voltage value detected immediately before is stored as the maximum voltage value Vmax.

  Further, in S23, the minimum voltage value Vmin2 of the detection signal output from the coil 36b of the pickup 36 next to the maximum voltage value Vmax is measured and stored. The minimum voltage value Vmin2 is measured in the same manner as the minimum voltage value Vmin1 is measured.

  In the next S24, the period T is measured from the time interval (phase difference) between the first minimum voltage value Vmin1 and the second minimum voltage value Vmin2, and the frequency of the basic waveform is calculated.

In S25, the noise component frequency 1 / Tn is calculated from the time interval Tn of the noise component included in the detection signal (noise component frequency calculating means) .

In S26, it is checked whether the frequency 1 / Tn of the noise component is larger than the abnormality determination value for the frequency 1 / T of the basic waveform. In S26, when the frequency 1 / Tn of the noise component is smaller than the abnormality determination value for the frequency 1 / T of the basic waveform, the process proceeds to S27, where the normal waveform is determined and the flow rate pulse is generated without correcting the waveform.

If the frequency 1 / Tn of the noise component is larger than the abnormality determination value for the frequency 1 / T of the basic waveform in S26, the process proceeds to S28, and the measurement waveform is determined from the frequency 1 / T of the basic waveform and the peak value of the measurement waveform. Correction is made to the obtained sine waveform ( correction means).

  Thus, even when noise is superimposed on the detection signal output from the pickup 36, the period T is measured from the time interval (phase difference) between the first minimum voltage value Vmin1 and the second minimum voltage value Vmin2, By calculating the frequency of the basic waveform, it is possible to determine whether there is an abnormality in a pseudo manner. Therefore, by comparing the frequency (or period) of the pseudo sine wave containing noise with the frequency (or period) of the regular signal, it becomes possible to determine the presence or absence of abnormality and is affected by noise. It is possible to measure from a small flow rate to a large flow rate without any problems.

  A modification of the second embodiment will be described. In the above embodiment, the voltage value of the detection signal detected by the flow rate measurement is compared with the voltage value of the normal signal to determine the presence or absence of abnormality. As a modified example, it is obtained from the frequency-voltage value characteristics of the normal signal. It is also possible to determine the presence or absence of abnormality by comparing the normal frequency with the measured voltage value and the measured frequency.

  In the above embodiment, a turbine type flow meter has been described as an example. However, the present invention uses a measurement system that detects the rotation of the rotor using a pickup and generates a flow rate pulse from the detection signal. Needless to say, the present invention can be applied to a flow meter other than a turbine type flow meter.

It is a figure which shows one Example of the turbine type flow meter which becomes this invention, (A) is a longitudinal cross-sectional view of a turbine type flow meter, (B) is a pressure distribution figure in a flow path. It is a figure which shows the flow volume measuring method by the impeller 16, (A) is a longitudinal cross-sectional view which shows the state by which the impeller 16 was floated, (B) is the detection output from the pick-up 36 corresponding to (A). It is a wave form diagram of a signal. 4 is a waveform diagram of a detection signal output from a pickup 36. FIG. 4 is a waveform diagram of a detection signal output from a pickup 36. FIG. It is a figure which shows the tolerance | permissible_range with respect to the graph A which shows a normal characteristic. 3 is a flowchart for explaining flow rate measurement control processing 1 executed by a control circuit 38; It is a figure which shows the modification of the pick-up. It is a figure which shows the waveform of the state on which the noise was superimposed on the detection signal output from the pickup. 4 is a flowchart for explaining a flow rate measurement control process 2 executed by a control circuit 38;

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Turbine type flow meter 12 Meter main body 14 Flow path 16 Impeller 18 Rotating shaft 24 Upstream side cone 26 Downstream side cone 30 Hub 32 Blade 36 Pickup 38 Control circuit 39 Memory

Claims (1)

A rotor formed of a magnetic material that rotates according to the flow rate of the fluid to be measured flowing in the flow path;
A pickup that forms a magnetic field in a region where the rotor rotates, detects a magnetic change accompanying the rotation of the rotor, and outputs a detection signal;
In a flowmeter comprising flow rate calculation means for calculating the flow rate of the fluid to be measured flowing in the flow path from the detection signal output from the pickup,
Voltage detection means for detecting a voltage value of a detection signal output from the pickup;
Period calculating means for calculating the period of the basic waveform from the minimum voltage value or the maximum voltage value of the detection signal obtained based on the voltage value detected by the voltage detecting means;
Noise component frequency calculation means for calculating the frequency of the noise component obtained based on the voltage value detected by the voltage detection means;
When the frequency of the noise component is larger than a predetermined abnormality judgment value, a correction means for correcting the measurement waveform of the detection signal to a sine waveform obtained from the frequency of the basic waveform and the peak value of the measurement waveform;
With
The flow rate calculation means measures the flow rate of the fluid to be measured flowing in the flow path based on the detection signal when the frequency of the noise component calculated by the noise component frequency calculation means is equal to or less than a predetermined abnormality determination value. flowmeter and said Rukoto to be measured.

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